Calling the Friendly Mechaniks,,,,

another old trick ( engine setting at idle)  is to spray starter fluid ( or other) in short bursts at various hoses and rubber gasket areas to see if it gets sucked in and changes the idle speed.

Post #'s have their PERKS 

Respect is earned, not dependent on post #...

whats the old saying about keeping YOUR MOUTH SHUT and letting people assume your an idiot, as compared to OPENING your mouth and REMOVING ALL DOUBT ?? 

A map sensor is a vacuum sensor. Have to find what is throwing it off.

Engine compression should be 180psi. Discrepancies in the readings across the 4 cyls and you may be having a timing chain issues. 

Starting fluid is a good idea to try to find leaks around the intake gasket as Steve said.

DiyDave wrote: Respect is earned, not dependent on post #...

I'll second that.

Despite all the whiz-bang technology touted, the ECM of even today's NEW machines are NOT in any way good diagnostic tools.  Without a healthy understanding of HOW the ECM determines a fault, the scanner's output is little more than a shot-in-the-dark. 

From a 'machine thinking' perspective, it can only see sensors, and can only control a few things.  It is programmed to primarily control fuel (by changing the pulse duration of injectors) and ignition (by changing the time of pulses triggering the ignition module(s).

So really, all it's doing from an 'active' sense, is marking time, and pulsing stuff.  The rest is just turning on and off other stuff like... the warning lights on the dash, the AC compressor clutch, the alternator field driver, and the radiator's electric cooling fan.

The SENSORs include MAP, they also usually have an air temperature, engine coolant temp sensor, a crankshaft position sensor, a camshaft phase sensor, a spark knock sensor, and a throttle position sensor.

Each of these sensors' data is gathered, and compared to 'data maps'... arrays of numbers corresponding to what the proper fuel and ignition outputs need to be for any given rpm and loadpoint... at any given engine coolant and ambient air temperature and pressure.

Sound simple?  It doesn't, but it actually IS.  The computer looks at the numbers for each sensor's output, and looks it up on a multidimentional 'map', then pulses injectors and fires spark plugs.

It's so simple, what could go wrong? 

Well, at 256,000 miles, just about ANYTHING can upset the apple cart.  As others noted, vacuum hoses, a PCV system leak, a bad ground... a skipped tooth on the timing belt... any ONE of those things.

The computer, however, reports an error code based on whatever SENSOR didn't match up with anything on it's data map.

And it tells you where it 'fell off' the map, either based on either whatever 'bad SENSOR SIGNAL' it read FIRST.... or whichever was the LAST sensor read before 'falling off' the data map.

It is MOST likely, that whatever problem you're having, is related to age and mile wear.  If you were in a less-arid environment, you'd have corrosion as a most likely.

Whatever you do, don't assume that the COMPUTER is actually smart enough to know what is REALLY wrong, because it isn't.  A really good scanner will likely give you a better translation of codes, and let you reset them, and retest, possibly see the ORDER of codes, but never assume the actual code is little more than a 'clue'.  Regular test tools (vacuum gauge, spray-stuff, and a well-tuned hearing-aid for vacuum leaks, compression tester for cyl seal health), a good volt-ohmmeter, and a good service and diagnostic manual on the car is what you really need.

Not really...  and I wouldn't be inclined to get sensors and actuators from a wrecking yard unless I knew-for-certain that the donor was extremely-low-mile and certainly NOT there because of the component.

The sensor that suffers the most wear, is the throttle position sensor... and it wears most in the right-off idle position, and at the position where it tends to sit at highway speeds.  Like the steering worm on a tractor, the TPS spends most of it's time working in one vicinity, while the rest goes mostly unused.

The MAP sensor is usually a peizoelectric device, air pressure causes a sandwich of dissimilar metals and a thin sheet of mica to flex, generating a slight voltage... a good shock in either pressure or physical (whack with a hammer, or long drop onto concrete floor) can cause them to go bad... but over time, the dissimilar sandwich will delaminate, and the thin mica sheet can fracture, then they become erratic.

Crankshaft and phase sensors come in several flavors, one of them is a 'hall effect' device, it's a transistor that, rather than responding to a signal voltage to amplify, it responds to a magnetic field.  Hall-effect devices can fail from being 'oversaturated' with magnetism, or frozen, or shocked, or bit with static electricity.  Another type is 'reluctance', which is a magnetic core with wire coil around it, just like the pickup on your Fender Telecaster... tooth comes by the polepiece, you get voltage swing at the output.  Just like on the guitar, the coils can fail from vibration over time, so they're usually potted in some sort of epoxy, that after a dozen years, slowly shrinks, and cracks, and you end up with the shrinking epoxy ripping the wires in two.

The Exhaust Oxygen Sensor (O2) is a chemical-balance device, it has two dissimilar metals spaced close together, and once at proper temperature, exhaust gasses passing by will generate a voltage based on the amount of oxygen present in the gasses.  In order for it to work properly, it's gotta stay CLEAN, as oil and carbon fouling will cause problems getting a good reading.  They're most likely to foul bad on cold startup, because a cold engine is belching out condensates and excess fuel until the combustion chamber temp comes up, and then they're a bit skunky 'till the crankcase oil temp gets to normal, as that oil is also holding condensation products.  To help make the O2 sensor last longer, there's a heating element in 'em, it forces the tip temperature up, so that it will help 'burn off' crud that's coming by.  Sometimes the heater works better than others, but as an engine gets older, and more blowby travels from the crankcase into the PCV system, there's more unburned crud coming down the tailpipe.  Most of the time, a new O2 sensor won't last too long, as the main problem is a plugged up Positive Crankcase Ventilation system.

There's a whole lot to know... and I'm not the guy that knows it all.

 Well when do we get the report of how good it worked  as weed killer or  was it fertilizer.  Or was it just to over run the stockholder with the homeless following that wonderful aroma.

Sorry Joe, back under my rock I go.